1. Field of the Invention
This invention relates to a dry, fine particle size particulate hydraulic cement composition, a method of forming a hydrocarbon liquid slurry using said composition, a method of forming a water slurry using said composition, and methods of utilizing said slurries.
2. Description of the Prior Art
Dahl, et al., in U.S. Pat. No. 5,238,064 disclose a method of using a fine particle size cement in a hydrocarbon slurry to prevent the flow of unwanted water from a subsurface formation into a wellbore. The relevant portion of Dahl, et al., is set out below.
Subterranean formations sometimes produce unwanted water from natural fractures as well as from fractures produced by forces applied deliberately or accidentally during production operations. It is known that such fractures provide a path of least resistance to the flow of fluid from a formation to a wellbore. When the fluid flowing in a fracture is primarily oil, the fracture is considered to be beneficial and thus desirable; however, when the fluid flowing in the fracture from the formation to the wellbore is primarily water the fracture is considered to be a problem and thus undesirable. By the method of this invention the undesirable fracture can be filled with fine cement to plug it and thereby terminate the flow of fluid therein.
The fine particle size cement of this invention can be placed in a subterranean fracture as well as in a high permeability zone of the formation by the application of conventional procedures. The cement itself, although it is highly reactive due to its small particle size, can be rendered temporarily non-reactive by preventing contact between it and water prior in time to actual placement of the cement into the fracture. Accordingly the fine cement of this invention is dispersed in a relatively low viscosity, relatively non-volatile liquid hydrocarbon, such as diesel oil, to form a pumpable slurry of cement in oil.
The dispersion of the cement in the non-volatile liquid hydrocarbon must be assisted by use of an appropriate surfactant, which is hereinafter more fully described. In this regard it has been discovered that a mixture of the fine cement of this invention with the liquid hydrocarbon, in the absence of a surfactant, produces a blend having a viscosity so high that the blend cannot be pumped by conventional means into the desired location in the formation. Use of the surfactant, as described below, results in a blend of cement in hydrocarbon having a sufficiently low viscosity to permit convenient conventional introduction of the blend into the desired location in the formation.
Furthermore, it has also been discovered that the high beneficial hydraulic activity of the fine particle size cement of this invention can be unduly reduced upon contact with a hydrocarbon, but that the problem can be avoided by use of the hereinafter further described surfactant.
Thus, the use of a surfactant is necessary to enable the production of a cement in hydrocarbon slurry having a sufficiently low viscosity to permit convenient placement in the desired zone, and to prevent the liquid hydrocarbon carrier from oil wetting the surface of the small particle size cement because such oil wetting would cause the fine cement to suffer a loss of hydraulic activity. The slurry is then introduced into the fracture.
After the slurry of cement and oil is in the fracture, water flowing in the fracture slowly contacts the cement to thereby render the cement reactive so as to initiate hydration, hardening and ultimate formation of a permanent plug in the fracture. By this technique the cement in the hydrocarbon/surfactant/cement slurry will only set when contacted by water in the fracture and thus will not set if the slurry enters a fracture containing oil. Accordingly, oil producing portions of a reservoir will remain relatively damage free.
As mentioned above, successful formulation of a cement in hydrocarbon oil slurry to obtain the goals set out above depends upon sufficient dispersion of the cement in the oil. In this regard, such a dispersion is obtained by combining a hydrocarbon liquid, such as diesel oil, a soluble hydrocarbon liquid surfactant, as hereinafter defined, and the fine particle size cement of this invention. The preferred order of blending of the ingredients involves adding the correct quantity of surfactant to the hydrocarbon liquid with thorough mixing and then slowly adding the cement to the oil/surfactant blend with continued mixing to obtain the desired slurry of uniform consistency.
The surfactant useful herein, which is a solution consisting of an aromatic sulfonic acid or a salt thereof dissolved in a low molecular weight alcohol, is mixed with a hydrocarbon liquid, such as diesel oil, in an amount in the range of from about 10 to about 25 and preferably about 20 gallons of surfactant solution per 1000 gallons of hydrocarbon liquid. The quantity of hydrocarbon liquid to be utilized is dependent upon the quantity of fine particle size cement employed and is in the range of from about 6 to about 10 gallons of hydrocarbon liquid per 100 pounds of fine cement. The amount of hydrocarbon liquid and surfactant utilized, within the scope of the above proportions, will determine the density of the resulting cement/hydrocarbon slurry wherein the slurry density is inversely proportional to the quantity of liquid. Accordingly, 4400 pounds of fine cement, 5.5 gallons of a preferred surfactant and 275 gallons of diesel will produce a slurry having a density of about 14.1 pounds per gallon while 4400 pounds of fine cement, 8.0 gallons of surfactant and 400 gallons of diesel will produce a slurry having a density of about 12.5 pounds per gallon.
The low viscosity, non-volatile hydrocarbon liquid useful herein can be an aliphatic compound, such as hexane, heptane or octane, an aromatic compound such as benzene, toluene or xylene and mixtures thereof such as kerosene, diesel oil, mineral oil and lubricating oil.
As mentioned previously, the surfactant includes, as an essential component, an aromatic sulfonic acid or a salt thereof. This component is sometimes referred to herein as the organic acid or salt component. The organic acid component is a compound identified by the formulas: ##STR1## wherein R.sub.1 is selected from linear alkyl groups having 12 carbon atoms or 16 to 24 carbon atoms and R.sub.2 and R.sub.3 are linear alkyl groups containing 12 carbon atoms.
Compounds within the scope of formulas (1) and (2) known to be useful herein are the acids themselves as well as the alkaline earth metal salts thereof. The preferred such salts are the calcium salts and the magnesium salts.
The preferred organic acid component of the surfactant of this invention is selected from the group consisting of calcium dodecylbenzene sulfonate, calcium didodecylbenzene sulfonate and calcium salts of benzenesulfonic acid having linear alkyl groups containing 16 to 24 carbon atoms. The most preferred is calcium dodecylbenzene sulfonate.
In a broader context the organic acid component is thought to include linear alkyl aromatic sulfonic acid, linear alkyl aromatic phosphonic acid, linear alkyl aromatic sulfonates and linear alkyl aromatic phosphonates having at least one linear alkyl group containing at least eight carbon atoms.
The low molecular weight alcohol solvent component of the surfactant solution is selected from aliphatic alcohols having in the range of from 1 to 5 carbon atoms wherein isopropanol is preferred.
The alcohol is present in the surfactant solution in the range of from about 20 to about 40 and preferably about 25 parts alcohol per 100 parts by volume of the surfactant solution.
The organic acid or salt component of the surfactant solution is present in the surfactant in the range of from about 60 to about 80 and preferably about 75 parts acid or salt per 100 parts by volume of the surfactant solution.
In view of the above, it is evident that Dahl, et al., teach that the surfactant solution is first blended with the hydrocarbon liquid with thorough mixing followed by slowly adding the cement to the oil/surfactant blend with continued mixing. Accordingly, Dahl, et al., limit their invention to the use of a cement-in-hydrocarbon slurry wherein the cement phase of the slurry does not harden unless the slurry contacts water. If the slurry does not contact water downhole, then the cement does not set and a waste disposal problem is presented as the slurry is recovered with formation fluids.
We have now discovered that the fine particle size cement disclosed by Dahl, et al., can first be placed in contact with the surfactant in required amounts and then stored in a dry state for an indefinite period of time without loss of hydraulic activity. The surfactant-treated cement, hereinafter called the "surfactant cement", can thereafter be mixed with a hydrocarbon liquid to shut off water to obtain the results disclosed by Dahl, et al. The surfactant cement also can be mixed directly with water to form a slurry of fine particle size cement in water to perform all of the various other functions disclosed in U.S. Pat. No. 5,238,064 with no substantial change of produced results. In short, merely by contacting the dry cement with the surfactant, instead of mixing dry cement in a previously prepared surfactant/hydrocarbon liquid blend, has effectively converted the cement employed from a single purpose to a multipurpose material.